1. Technical Field
The inventive concept relates to a semiconductor device, and more particularly, to a vertical memory device and a method of fabricating the same.
2. Related Art
The distribution rate of portable dig devices has been increasing day by day and ultra-high integration, ultra-high speed, and ultra-low power of memory devices, which are built in a limited size to process large capacity of data with high speed, have been required.
Studies on vertical memory devices have been actively progressed to meet these demands. Recently, the vertical structures are introduced into resistive memory devices that are spotlighted as next-generation memory devices.
The resistive memory devices are devices that select a memory cell through an access element, change a resistance state of a data storage material electrically connected to the access element, and store data. There are typically phase-change random access memories (PRAMs), resistance RAMs (ReRAMs), magnetoresistive RAMs (MRAMs), and the like as the resistive memory devices.
Diodes or transistors may be employed as the access element of the resistive memory devices. In particular, the threshold voltage of the transistors is controlled to be low as compared with the diodes and thus the operation voltage thereof can be reduced, and the transistors have received attention again as the access element of the resistive memory devices by applying the vertical structure thereto.
That is, since the voltage of 1.1 V or more has to be applied to the diodes, there is a limitation to reduce an operation voltage of the diodes. Further, when the diodes are formed on a word line, a resistance of the word line is varied according to positions of the cells to cause word line to be bounced.
Since transistors in the related art are formed in a horizontal structure, the reduction rate is restricted. However, the vertical transistors can sufficiently ensure current drivability in the limited channel area.